Previous implementation used a dedicated download mechanism: retrieve
them from download sites (but without checksum checks), cache them locally
and detect if they were available locally.

New implementation relies on the Maven dependency resolution. This
  - makes the pom simpler (no antrun task, nor dedicated caching), in particular
  remove dependency on ant-contrib
  - cache, checksum checks are deferred to Maven --> safer builds

In addition, fix community tomcat assembly (remove leading /) that were
useless and generated warning when building on windows

Plus some minor fixes:
  - fix warning generated by parent not in the root folder (set no relative
     path)
  - set encoding to UTF-8 for reproducible builds
  - wildfly bundle community: remove the deploy plugin configuration as
     it is managed at top level globally in the parent of the project and
     configured using a property set to not deploy the module
  - git ignore: correctly ignore node resources


Covers [BS-19060](https://bonitasoft.atlassian.net/browse/BS-19060)